We have systematically studied the etching characteristics of SiO2 layers using an inductively coupled plasma (ICP) etching system. The surface morphology, etch rate, selectivity, and sidewall angle have been studied as a function of varying pressure, gas flow rate, capacitive r.f. power, and inductive r.f. power. Chrome was used as an etch mask, and CF4 or SF6 was used as a reactive gas. Using either one of the gases, excellent results were obtained. Depths exceeding 6 mu m were etched with few observable defects and near vertical sidewalls. This process was applied to make SiO2 waveguides for planar lightwave circuits.